Why does a boat crack?

[traderdavel]

My friends Larson, (1999 290) seems to have developed cracks in different areas. One of the cleats has a 3" crack near it, the floor has some cracks to it, (some are near where a molded seat meets the floor). Near the water fill there is another crack. They don't look to bad, nothing chipping away, and they are hairline cracks, (he described it as spider webs) - but just not sure what could cause it, how to fix it. No spongy / soft spots.

Any thoughts.

 

[TheLucille]

Re: Why does a boat crack?

Some cracks are structural from flexing and the fact that cracks often form where there is a highly stressed area of the hull, especially if there are holes drilled (like for cleats). Highly stressed areas need to be strong yet somewhat flexible.

Also, some cracks are completely non-structural, and exist only because the gelcoat shrinks and it has to "tear" somewhere. I hear this often happens on black painted surfaces due to the heat buildup.

 

[tboltmike]

Re: Why does a boat crack?

In addtion to the above, sharp junctures in the design cause stress risers. Also fatigue at flex points.

 

[marine4003]

Re: Why does a boat crack?

When most boats are built, chopped fiberglass is sprayed into a "mold" then removed and then gelcoat is sprayed over the 'glass...if its not allowed to cure correctly..it becomes brittle, structurally, theres no problem,as long as its hairline, the hulls that suffer hairline cracks at stress points are generally the result of hurrying the process at the factory, alot of orders , demand for the particular model..things aren't allowed to cure properly...Brittle GC..= Cracks.

 

[emilime75]

Re: Why does a boat crack?

When most boats are built, chopped fiberglass is sprayed into a "mold" then removed and then gelcoat is sprayed over the 'glass.

I always thought it was the other way around, as in the gel coat is sprayed into the mold first, then the fiberglass goes over it. Either way, small web cracks in the gel coat are not uncommon, especially around stress areas like cleats simply because holes were drilled to mount that cleat, same goes for the water fill.

 

[oops!]

Re: Why does a boat crack?

uh.....actually......when they make a boat....they spray gellcoat into the mold.....then a layer of better resin and chopped strand....then a full chopper gun spray of laminating resin.....the gell coat needs a hard surface to cure to....that way when the pull the boat from the mold....it is shiney and smooth.

now....if the catylisation rate is incorrect, or the gellcoat is sprayed too thick or too thinn.....stress cracks will occure ....they look like spider webs ....this is called crazing.

however.......larsons are prone to this......i have seen several that have stress cracks lately....newer boats too.....i just did a tower on a 06 that had really big stress cracks in it......i told the owner to sell the boat in a season or two cause it would just get worse...(he was a really picky type of person)
i repaired a few crazing spots for free for him.....

the crazing could also be caused by the curved surfaces of the larson.....in the mold...the gellcoat tends to collect in the rounded areas and corners..making the gellcoat thicker than it should be.

hope that helps
cheers
oops

 

[oops!]

Re: Why does a boat crack?

I always thought it was the other way around, as in the gel coat is sprayed into the mold first, then the fiberglass goes over it.

this is correct........take a basic mold....spray pva into it...(a release agent) then in goes the gellcoat

 

[dingbat]

Re: Why does a boat crack?

uh.....actually......when they make a boat....they spray gellcoat into the mold.....then a layer of better resin and chopped strand....then a full chopper gun spray of laminating resin.....the gell coat needs a hard surface to cure to....that way when the pull the boat from the mold....it is shiney and smooth.

oops

You mean all boats are not 100% hand laid-up?

 

[traderdavel]

Re: Why does a boat crack?

This helps -thank you all - but it brings a couple of more questions. Would you stay away from a boat because of this, should it be repaired, or is it like wrinkles on a persons skin? Non- damaging, just noticeable.

Thanks again - always great help on this forum!

 

[otec465]

Re: Why does a boat crack?

just his one of a kind boat

 

[salty87]

Re: Why does a boat crack?

This helps -thank you all - but it brings a couple of more questions. Would you stay away from a boat because of this, should it be repaired, or is it like wrinkles on a persons skin? Non- damaging, just noticeable.

Thanks again - always great help on this forum!

they're mainly cosmetic although lots of time you can figure out what went wrong....thru hulls can be tightened too much, stressing, etc.

if your boat is new, i'd be concerned because the cracks could keep running. if it's old and cracks have just developed, might want to try to figure out why. if it's old and the cracks have never gotten worse, not much to worry about.

lots of times the cracks will come back after being repaired unless the underlying stress issue is resolved.

 

[marine4003]

Re: Why does a boat crack?

uh.....actually......when they make a boat....they spray gellcoat into the mold.....then a layer of better resin and chopped strand....then a full chopper gun spray of laminating resin.....the gell coat needs a hard surface to cure to....that way when the pull the boat from the mold....it is shiney and smooth.

now....if the catylisation rate is incorrect, or the gellcoat is sprayed too thick or too thinn.....stress cracks will occure ....they look like spider webs ....this is called crazing.

however.......larsons are prone to this......i have seen several that have stress cracks lately....newer boats too.....i just did a tower on a 06 that had really big stress cracks in it......i told the owner to sell the boat in a season or two cause it would just get worse...(he was a really picky type of person)
i repaired a few crazing spots for free for him.....

the crazing could also be caused by the curved surfaces of the larson.....in the mold...the gellcoat tends to collect in the rounded areas and corners..making the gellcoat thicker than it should be.

hope that helps
cheers
oops

I had a 67 hour week...total brain fart. Thanks for clarifying ..

 

[skargo]

Re: Why does a boat crack?

I've found that running a drill in reverse to start a hole, THEN going in forward helps prevent cracks when drilling necessary holes.

 

[traderdavel]

Re: Why does a boat crack?

Should hairline cracks be fixed? How is it done? What does it cost?

 

[Bifflefan]

Re: Why does a boat crack?

You mean all boats are not 100% hand laid-up?

from an article i read just the other day on here, they only ones that are not sprayed in these days are Bertrams. hence the reason they cost alot.
that being said from the article they are not solid fiberglass eather, they have some sort of puddy looking stuff behind the gelcoat and then a thin layer of glass, and thats it.
ill try to find that article and post it here. if i cant maybe do a search and you can find it. it was a little scary reading it.

 

[metriccrescentwrench]

Re: Why does a boat crack?

IMHO, alot of these types of small cracks I'd chalk up to quality (both of the design and manufacturing process).

Checkmate boats, for instance, are all hand laid using fiberglass cloth. I just bought a 30 year old Checkmate and it has zero cracks and the original gelcoat is still in fantastic condition. Good design and quality workmanship.